1. Field of the Invention
This invention relates to a surge detection system of a gas turbine aeroengine, more specifically to a system for detecting a surge occurred at a compressor of a gas turbine aeroengine.
2. Description of the Related Art
In gas turbine aeroengines, if the combustion gas temperature rises sharply because, for example, an increased amount of fuel flow at acceleration is excessive relative to the air flow amount, a compressor rotor blade or blades may sometimes stall. When the stall is serious, the stator vane(s) may also stall and the stall condition may be transmitted to adjacent blades one after another, resulting in a surge.
It should be noted that xe2x80x9csurgexe2x80x9d and xe2x80x9cstallxe2x80x9d are used in the following to indicate the same meaning. In other words, a stall occurred at a compressor blade or at a limited group thereof and a surge caused by extensive blade stalling will generally be called xe2x80x9csurgexe2x80x9d
Since a severe surge may propagate an airframe vibration and may sometimes damage blades, various surge detection techniques have hitherto been proposed.
For example, Japanese Laid-Open Patent Application No. Sho 58(1983)-57098 teaches detecting the occurrence of surge if the absolute value of change of the compressor outlet pressure with respect to time (the absolute value of the differential of the compressor outlet pressure) is greater than a threshold value.
U.S. Pat. No. 4,603,546 proposes detecting the occurrence of surge if the ratio between the compressor outlet pressure and the change thereof with respect to time (the differential thereof) is less than a threshold value.
Japanese Laid-Open Patent Application No. Sho 59(1984)-7738 discloses detecting the occurrence of surge when the ratio between the high-pressure turbine speed and the turbine inlet temperature (gas temperature downstream of the combustion chamber) is less than a threshold value.
U.S. Pat. No. 4,581,888 discloses detecting the surge when the ratio between the high-pressure turbine speed (corrected) and the ratio between the compressor outlet pressure and the fan inlet pressure is greater than a threshold value.
Thus, four kinds of surge detection techniques have been proposed. However, since these four kinds of techniques can not distinguish the surge from engine deceleration, additional determination action of whether the engine is accelerating is needed. Moreover, these methods can not distinguish the surge from misfiring under acceleration.
The drawbacks in these prior art techniques will be explained in detail with reference to the drawings.
As regards the technique taught by Japanese Laid-Open Patent Application No. Sho 58(1983)-57098, as shown in FIG. 7A, it uses the absolute value of the differential of the compressor outlet pressure (illustrated as P3dot in the figure) as a surge detection parameter. Since this parameter fluctuates greatly even under normal condition, this technique can not discriminate the surge from the normal (non-surge) condition. Moreover, as shown in FIG. 7B, it may erroneously detect misfiring or deceleration as a surge.
It should be noted here that FIGS. 7A and 7B are simulation test data. FIG. 7A shows conditions including no surge (normal condition), a slight surge and a serious (large) surge, while FIG. 7B shows conditions including a slight surge, a serious surge, a deceleration and a misfiring. In FIGS. 7A and 7B, the abscissas indicate time [sec.]. These will be the same in the other figures.
As regards the technique proposed in U.S. Pat. No. 4,603,546, as shown in FIG. 8A, it uses the ratio between the compressor outlet pressure (illustrated as P3) and the differential of the compressor outlet pressure (illustrated as P3dot). This configuration can improve the accuracy of distinction between the normal condition and the surge condition.
Although the measurement fluctuation under normal conditions becomes less than that by the technique illustrated in FIG. 7A, it is still large. Thus, to use only a parameter relating to the compressor outlet pressure for surge detection will inevitably lead erroneous results. Moreover, as shown in FIG. 8A, this technique may erroneously detect the misfiring or deceleration as a surge.
As regards the technique mentioned in Japanese Laid-Open Patent Application No. Sho 59(1984)-7738, as illustrated in FIG. 9A, since this uses the ratio between the high-pressure turbine speed (shown as xe2x80x9cN2xe2x80x9d) and the turbine inlet temperature (gas temperature downstream of the combustion chamber; shown as xe2x80x9cT45xe2x80x9d), this method can not detect a slight surge accompanying no turbine inlet temperature change. Moreover, this method needs a relative long time to detect a serious surge with turbine inlet temperature change. In addition, as shown in FIG. 9B, this method may erroneously detect misfiring as a surge.
As regards the technique disclosed in US Patent No. 4,581,888, as illustrated in FIG. 10A, this uses the ratio between the corrected value of the high-pressure turbine speed (shown as xe2x80x9cN2xe2x80x9d), and the ratio between the compressor outlet pressure P3 and the fan inlet pressure (shown as xe2x80x9cP1xe2x80x9d). Since difference in these parameters between the normal condition and the surge condition is small, the technique is not satisfactory in detection accuracy. And, as shown in FIG. 10B, it may also erroneously detect misfiring as a surge.
A first object of this invention is therefore to overcome the problems of the prior art techniques by providing a surge detection system of a gas turbine aeroengine that can accurately detect a surge occurred at the compressor and even a magnitude or degree of the surge occurred, without need for engine acceleration detection.
A second object of this invention is therefore to overcome the problems of the prior art techniques by providing a surge detection system of a gas turbine aeroengine that can accurately detect a surge occurred at the compressor and can conduct a corrective control to suppress the surge if occurred.
For realizing these object, the present invention provides a system for detecting a surge occurred at a compressor of a gas turbine aeroengine having a turbine connected to the compressor, comprising: compressor outlet pressure detecting means for detecting an outlet pressure of the compressor; turbine inlet temperature detecting means for detecting an inlet temperature of the turbine; compressor outlet pressure change parameter determining means for determining a first parameter indicative of change of the compressor outlet pressure based on at least the detected compressor outlet pressure; turbine inlet temperature change parameter determining means for determining a second parameter indicative of change of the turbine inlet temperature based on at least the detected turbine inlet temperature; surge detection parameter determining means for determining a third parameter for surge detection based on the determined first and second parameters; parameter comparing means for comparing the third parameter with a threshold value; and surge detecting means for detecting the surge occurred at the compressor based on a result of the comparison.